1. Technical Field of the Invention
The present invention relates in general to the to mobile radio communications field and, in particular, to a method and system for use in determining the geographical position of a mobile radio terminal ("geolocation") in a mobile radio system following a Code Division Multiple Access (CDMA) standard.
2. Description of Related Art
Commonly-assigned U.S. patent applications Ser. Nos. (Attorney docket Nos. 27946-00353 and 27946-00354) filed on Nov. 26, 1997 disclose methods for use in performing position determinations in a Time Division Multiple Access (TDMA) system. The methods include the steps of ordering an intra-cell handoff, receiving in three radio base stations (BSs) repeated access bursts from a mobile radio terminal (mobile station or MS) whose position is to be determined, in each RS incoherently integrating the squared absolute values of those bursts, and determining the uplink time-of-arrival (TOA) by statistically evaluating the TOA results from randomly selected groups of these bursts. The uplink TOA information is used to derive the position of the MS.
The IS-95 standard (CDMA) published by the Electronics Industry Association/Telecommunications Industry Association (EIA/TIA) discloses the use of a spreading code for TOA measurements in conjunction with determining the position of a MS. The spreading code used is a long code (LC) with a periodicity of thousands of chips, but it is designed for other uses than position determination. As such, the information superimposed on this LC must be known when using it for position determination purposes.
A drawback of the first-mentioned position determination method using TOA information is that it is not suitable for use in CDMA systems, because received information in CDMA systems is superimposed on the spreading codes. A drawback of the second-mentioned method is that it is not optimized for use in making position determinations. As such, since determining the position of mobile terminals has become very important in the mobile communications field, it is just as important to have a method that is optimized for this particular purpose.